The role of mesoscale meteorology in modulating the ²²²Rn concentrations in Huelva (Spain) – impact of phosphogypsum piles

The combined analysis of ²²²Rn activity concentrations and mesoscale meteorological conditions at Huelva city (Spain) was addressed in this study to understand the potential impact of phosphogypsum piles on the ²²²Rn activity concentrations registered at this area. Hourly mean data from April 2012 to February 2013 registered at two sampling sites (Huelva city and in the background station of El Arenosillo, located 27 km to the south-east) have been used in the study. The results of the present study showed a large difference in mean radon concentrations between the two stations during the sampling period, 6.3 ± 0.4 Bq m⁻³ at Huelva and 3.0 ± 0.2 Bq m⁻³ at El Arenosillo. The analysis has demonstrated that hourly ²²²Rn concentrations at Huelva city above 22 Bq m⁻³, with nocturnal peaks up to 50 Bq/m³, mainly coincided with the occurrence of a pure sea-land breeze cycle. Mesoscale circulations in this region are mainly characterized by two patterns of sea-land breeze, pure and non-pure, with the phosphosypsum piles directly upstream (south) of the city during the afternoon on pure sea-breeze days. The difference between mean ²²²Rn activity concentrations at Huelva city were 9.9 ± 1.5 Bq m⁻³ for the pure pattern and 3.3 ± 0.5 Bq m⁻³ for the non-pure pattern, while in the background station concentrations were 3.9 ± 0.4 Bq m⁻³ and 2.8 ± 0.4 Bq m⁻³ respectively. Considering these large differences, a detailed analysis of composites and case studies of representative sea-land breeze cycles of both types and their impact on ²²²Rn activity concentration was performed. The results suggested that the presence of the phosphogypsum piles was necessary in order to justify the high ²²²Rn activity concentrations observed at Huelva compared with the background station in the afternoons on pure sea breeze days (1.5–2.0 Bq m⁻³). On the other hand, large night time differences between the two sites on these days were likely to be associated with a combination of shallow density currents travelling down the Guadalquivir valley and, again, the presence of phosphogypsum piles. The results have demonstrated a significant impact of the phosphogypsum piles on ²²²Rn activity concentrations in Huelva city during the occurrence of pure sea breeze days. - Highlights: • Analysis of meteorological impact on high ²²²Rn activity concentrations. • Identify the impact of phosphogypsum piles on ²²²Rn concentrations. • Temporal and spatial variability of ²²²Rn during sea-land breeze circulations. • Different impact of sea-land breezes on ²²²Rn activity concentrations